Merlin has broad tumor-suppressor functions as its mutations have been identified in multiple benign tumors and malignant cancers. In all schwannomas, the majority of meningiomas and 1/3 of ependymomas Merlin loss is causative. In neurofibromatosis type 2, a dominantly inherited tumor disease because of the loss of Merlin, patients suffer from multiple nervous system tumors and die on average around age 40. Chemotherapy is not effective and tumor localization and multiplicity make surgery and radiosurgery challenging and morbidity is often considerable. Thus, a new therapeutic approach is needed for these tumors. Using a primary human in vitro model for Merlin-deficient tumors, we report that the Ras/Raf/mitogen-activated protein, extracellular signal-regulated kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) scaffold, kinase suppressor of Ras 1 (KSR1), has a vital role in promoting schwannomas development. We show that KSR1 overexpression is involved in many pathological phenotypes caused by Merlin loss, namely multipolar morphology, enhanced cell–matrix adhesion, focal adhesion and, most importantly, increased proliferation and survival. Our data demonstrate that KSR1 has a wider role than MEK1/2 in the development of schwannomas because adhesion is more dependent on KSR1 than MEK1/2. Immunoprecipitation analysis reveals that KSR1 is a novel binding partner of Merlin, which suppresses KSR1’s function by inhibiting the binding between KSR1 and c-Raf. Our proteomic analysis also demonstrates that KSR1 interacts with several Merlin downstream effectors, including E3 ubiquitin ligase CRL4DCAF1. Further functional studies suggests that KSR1 and DCAF1 may co-operate to regulate schwannomas formation. Taken together, these findings suggest that KSR1 serves as a potential therapeutic target for Merlin-deficient tumors.

TAM family receptor tyrosine kinases comprising Tyro3 (Sky), Axl, and Mer are overexpressed in some cancers, correlate with multidrug resistance and contribute to tumourigenesis by regulating invasion, angiogenesis, cell survival and tumour growth. Mutations in the gene coding for a tumour suppressor merlin cause development of multiple tumours of the nervous system such as schwannomas, meningiomas and ependymomas occurring spontaneously or as part of a hereditary disease neurofibromatosis type 2. The benign character of merlin-deficient tumours makes them less responsive to chemotherapy. We previously showed that, amongst other growth factor receptors, TAM family receptors (Tyro3, Axl and Mer) are significantly overexpressed in schwannoma tissues. As Axl is negatively regulated by merlin and positively regulated by E3 ubiquitin ligase CRL4DCAF1, previously shown to be a key regulator in schwannoma growth we hypothesized that Axl is a good target to study in merlin-deficient tumours. Moreover, Axl positively regulates the oncogene Yes-associated protein, which is known to be under merlin regulation in schwannoma and is involved in increased proliferation of merlin-deficient meningioma and mesothelioma. Here, we demonstrated strong overexpression and activation of Axl receptor as well as its ligand Gas6 in human schwannoma primary cells compared to normal Schwann cells. We show that Gas6 is mitogenic and increases schwannoma cell-matrix adhesion and survival acting via Axl in schwannoma cells. Stimulation of the Gas6/Axl signalling pathway recruits Src, focal adhesion kinase (FAK) and NFκB. We showed that NFκB mediates Gas6/Axl-mediated overexpression of survivin, cyclin D1 and FAK, leading to enhanced survival, cell-matrix adhesion and proliferation of schwannoma. We conclude that Axl/FAK/Src/NFκB pathway is relevant in merlin-deficient tumours and is a potential therapeutic target for schwannoma and other merlin-deficient tumours.

INTRODUCTION: The translocator protein (TSPO) is a 18 kDa mitochondrial molecule associated with neuroinflammation and over-expressed in several brain diseases. 11C-(R)PK11195 is a specific ligand of TSPO for PET studies. We investigated the in vivo TSPO expression in high- and low-grade gliomas using 11C-(R)PK11195 PET, and applied it in guiding tumour biopsies. METHOD: 24 patients underwent volumetric MRI and dynamic 11C-(R)PK11195 PET scans. Reference tissue input function was obtained from the grey matter of cerebellum to determine the 11C-(R)PK11195 uptake in the tumours and the mirrored regions of interest (ROIs) in the contralateral hemispheres. Co-registered MR/PET images were used to guide tumour biopsies prior to surgical debulking, with high and/or low 11C-(R)PK11195 uptake foci defined as biopsy targets. Biopsy specimens were assessed for TSPO expression by immunohistochemical staining. RESULTS: In low-grade gliomas (14 cases), 11C-(R)PK11195 uptake within the tumours was lower than the contralateral ROIs (p = 0.001); sporadic high uptake foci were found in 8 tumours. In high-grade gliomas, 7 out of the 10 tumours showed higher uptake than the contralateral ROIs (p = 0.016), 4 of which displayed intensive 11C-(R)PK11195 signal despite only minor contrast enhancement on the MRI. There was low 11C-(R)PK11195 uptake and no contrast enhancement in 3 anaplastic asctrocytomas. Immunostains on tissue sections confirmed variable TSPO expression in neoplastic cells and activated microglia/macrophages. CONCLUSION: TSPO expression is decreased in low-grade gliomas and increased in most high-grade gliomas. TSPO expression within gliomas is inhomogeneous as detected by 11C-(R)PK11195 PET and confirmed by immunohistochemistry.

INTRODUCTION: Substituted indoles and related structures have been shown to exhibit potent anticancer activity against breast cancer cell lines. Here, the effects of structurally similar substituted indoles against the human glial cancer cell lines, 1321N1 and U87MG, have been investigated by comparing the effects of these compounds to conventional anti cancer drugs. METHODS: Cell viability in the presence of the test compounds was measured using an MTS assay and corroborated by an ATP cell proliferation assay as well as a Trypan blue exclusion test. The significance of reactive oxygen species (ROS) in the process was determined using an Image-iT® LIVE ROS kit from Invitrogen. RESULTS: Both cell lines were treated with four commercial anticancer drugs and IC50 values were only reached at concentrations of 20 µM for cisplatin and 50 µM for gemcitabine over 48hrs on the 1321N1 cell line. However, the more malignant U87MG cell line was resistant to all the drugs, except for cisplatin where the IC50 value was reached at 300 µM after treatment for 48hrs. Similar studies were carried out with various substituted indoles and the cytotoxicity results on both cell lines showed that the IC50 value was reached within 90 minutes for the most potent compound at a concentration of 600 µM (1321N1) and 800 µM (U87MG). The idea that the mechanism of action of these compounds may work through the generation of ROS was investigated and this was confirmed over a similar time course using a suitable fluorogenic marker. Moreover, it was shown that the addition of an antioxidant (ascorbic acid) abolished the potency of the most active compound. CONCLUSION: Here, it has been demonstrated that certain substituted indoles are able to have a rapid, deleterious effect on the viability of two glioma cell lines and indicated that ROS generation may induce cell death.